1. Field of the Invention
The present invention relates to a data communication network, and more particularly to a communication structure and method for incorporating fault-tolerance in a content-induced transaction overlap (CITO) system.
2. Description of the Background
All communication systems are subject to errors in data transmission due to hardware failures, noise, etc. The corruption of data resulting from these transmission errors is a significant problem. In addition, the semiconductor devices used in such communication systems may contain fabrication defects which contribute to errors in data transmission. In this case, disposal of the responsible component is the typical remedy. However, designers are finding ways to make semiconductor devices fault-tolerant in an effort to increase operational reliability and manufacturing yield.
The above-described problem of data transmission errors may be corrected using the well-known concept of error-corrective coding. Error-corrective coding may be implemented in a variety of ways ranging from simple parity checking to more sophisticated schemes having broader error correction capabilities. For instance, to increase the reliability of a communication system having a plurality of transceivers, the system can be designed to use multiple voting logic. This is accomplished by coupling each transceiver to a plurality of mediators. Counterpart data is sent from each transceiver to each of its connected mediators, and the mediators compare the received data to insure its consistency. The system becomes more reliable as the number of replicate data increases. For instance, FIG. 1 illustrates a system arranged in a "latin square" where each transceiver T.sub.1-16 communicates each bit of data in triplicate to three mediators M.sub.X1-4, M.sub.Y1-4 and M.sub.Z1-4. If the data bit is a logic "1", the three mediators should receive a &lt;1,1,1&gt;. Otherwise a transmission error has obviously occurred. In the case of a transmission error the mediators may "vote", whereby the data is interpreted on a two-out-of-three vote basis. This is known as "multiple voting logic". Alternately, the mediators may request that the data be retransmitted. Either way, the reliability is clearly increased.
In addition to providing a solution for transmission errors, the "latin square" of FIG. 1 make further economies possible. It is well-known that the manufacturing yield of semiconductor devices can be dramatically increased if fault-tolerant devices are designed with redundant circuits which can be substituted for defective circuits.
Unfortunately, multiple voting logic requires at least three data bits. This necessitates a three-dimensional matrix configuration as in FIG. 1 which requires a complex printed circuit board. Moreover, detecting and correcting multiple faults becomes rather complicated.
The present invention introduces error-corrective coding in a content-induced transaction overlap (CITO) communication system, and indeed, illustrates how the CITO protocol lends itself to the concept of error-correction. The same increased reliability as in the latin square arrangement of FIG. 1 is achieved with a simpler two-dimensional matrix arrangement and a unique adaptation of the CITO protocol. The present invention also provides a fault-tolerant redundant architecture for by-passing error-causing faults.
The CITO communication protocol is disclosed in U.S. Pat. No. 4,493,074 issued to Walter et al. (herein incorporated by reference). CITO is a combined communication protocol and method for compressing data to be sent from a plurality of senders over a single serial communication channel. The CITO protocol overlaps redundant data sent by different senders so that the total transmission time for all data is reduced. The efficiencies gained by use of the CITO protocol are significant. It would be a further advantage if CITO-based semiconductor devices could be made more reliable by use of error-corrective coding, and fault-tolerant by use of redundancy circuits.